04_Kovacevic.indd 53 Kovačević Galović et al.: Geochemical discrimination of Early Palaeogene bauxites in Croatia �AB STRA CT Two discriminant function models were created in order to distinguish between major- and trace-element geochem- ical patterns typical of Lower Palaeogene (Palaeocene, Pc) bauxites formed on the portion of the carbonate platform comprising the Karst or External Dinarides. Four groups of bauxites from Istria, North Adriatic Islands, North Dal- matia and Central Dalmatia have been distinguished, according to their specifi c combinations of major and trace el- ements, characteristic conditions of formation, and processes prevailing in the karst environment during subaerial exposure of the carbonate platform. Typically, in both models the fi rst discriminant function explains most of the sys- tem variability. However, the trace-element model proves itself as a more helpful predictive tool, representing the straightforward example of classifi cation of the samples into four pre-defi ned groups of Pc bauxites. Generally, both models follow a characteristic trend in geochemical signature related to the recent geographical position of the baux- ite deposits, namely a decrease in K2O and an increase in the Cr content in a SE direction (from Istria to Dalmatia). This was most probably the result of environmental conditions during the AdCP Cretaceous-Palaeogene emergent stage (Istria), and emplacement of parent rocks (ophiolite belt) supplying the necessary material for bauxite genesis (Central Dalmatia). Keywords: Bauxite; Adriatic Carbonate platform; Dinarides; Geochemistry; Discriminant function model Geochemical discrimination of Early Palaeogene bauxites in Croatia � Erli Kovačević Galović, Nikolina Ilijanić, Zoran Peh, Slobodan Miko and Ozren Hasan Croatian Geological Survey, Sachsova 2, P.O. Box 268, HR-10000 Zagreb, Croatia; (corresponding author: ekovacevic@hgi-cgs.hr) doi: 104154/gc.2012.04 Geologia Croatica 65/1 53–65 6 Figs. 6 Tabs. Zagreb 2012 Geologia CroaticaGeologia Croatica 1. INTRODUCTION Unlike many other types of ores and raw materials, bauxites were for a long time treated only as an aluminum ore, with all research efforts focused on the assessment of conditions of their detection, exploitation and refi nement. In spite of a great number of mineralogical and chemical analyses (albeit only partial in most cases), from bauxite deposits and occur- rences in Croatia being available in various studies and pro- fessional reports, bauxite genesis, particularly in relation to the adjacent karst (palaeo)environment and its tectonostrati- graphic constraints, was largely underestimated. Only lately, have models of the orogenic evolution of the Adriatic (Adri- atic–Dinaric) Carbonate Platform (AdCP) with special ref- erence to External Dinarides of the NE Adriatic region un- derlined the importance of a number of hiatuses of variable duration marked by bauxitic deposits (VLAHOVIĆ et al., 2005; KORBAR, 2009). Since bauxites are now well recog- nized as tectonic and climatic event markers at regional un- conformities, these investigations call for additional correla- tive studies within and across different stratigraphic hori zons, bearing in mind that clearly expressed emergent surfaces set the stage for the resonant interplay of tectonics, volcanism, eustasy and climate on various parts of the carbonate platform (D’ARGENIO & MINDSZENTY, 1995). Such a complex bauxite research seems indispensable in the light of the new lithostratigraphic scheme that became the basis for regional correlation studies within the entire region of the Croatian Karst Dinarides during the last two decades (e.g. MATIČEC et al., 1996; TIŠLJAR et al., 2002; VLA HOVIĆ et al., 2002; DRAGIČEVIĆ & VELIĆ, 2002). The amassed data in the plentiful literature on Croatian bauxites (e.g. ŠINKOVEC, 1973; SAKAČ et al., 1987; ŠINKO VEC & SAKAČ, 1981; ŠUŠNJARA et al., 1990; SAKAČ et al., 1984; ŠINKOVEC et al., 1994) is largely confi ned within the limits of particu- lar deposits, stratigraphic horizons, or local unconformities, Geologia Croatica 54 Geologia Croatica 65/1 but has immense potential indispensable in building regional models of platform evolution, except for rarer works address- ing a wider scope (e.g. SAKAČ & ŠINKOVEC, 1991). Croatian bauxites are hosted in carbonate rocks marking regional unconformities between several stratigraphic levels, of which the Upper Cretaceous – Lower Palaeogene hiatus can be singled out as a major one. In some parts of the AdCP (Istrian karst) emergence was uncharacteristically long, from as far back as the Lower Cretaceous (MATIČEC et al., 1996; Croatian Geological Survey, 2009), while elsewhere it was much shorter. The extent of subaerial exposure during the stratigraphic gaps is of particular importance in understand- ing the origin of bauxites, which is why the geochemical and mineralogical signature has much to say about the interven- ing processes prevailing on the emergent carbonate platform. The Lower Palaeogene (Palaeocene, Pc) bauxites are specifi - cally targeted for this purpose owing to their variable time span of emplacement (Lower Cretaceous to Lower Eocene) within the AdCP (from NE to SE), and assumed differences in geochemical signal received during exposure. Accord- ingly, the main purpose of this investigation was to assess the geochemical contrast (aided by qualitative mineralogi- cal analysis) among the different groups of Pc bauxites pre- viously defi ned in relation to their palaeographical/palaeo- tectonic settings (Fig. 1) To this effect, a multivariate statistical assessment of a primary geochemical pattern dis- tinguishing between samples from Istria, the North Adriatic islands, North Dalmatia (Drniš area) and Central Dalmatia (Imotski area) was performed, preferring multiple discrimi- nant analysis (MDA) as the most helpful mathematical tool. The latter is employed as a method of data reduction and or- ganization which offers a quick, simple and effective means of clarifying signifi cant groupings and trends among envi- ronmentally distinct sediment samples, in this case solely on the basis of their geochemical composition. 2. MATERIALS AND METHODS 2.1. Geological setting The area of the Croatian Karst (External or Outer) Dinarides is a thick carbonate succession deposited from the Middle Permian (or even Upper Carboniferous) to the Eocene on platforms of different ages, type and palaeogeographical set- ting. The evolution of the Karst Dinarides area started on an epeiric carbonate platform along the northern Gondwana margin with a signifi cant deposition of mixed carbonate-si- liciclastic sediments in the Permian, and mostly siliciclastic deposits in the Early Triassic (VLAHOVIĆ et al., 2002). In the Middle Triassic, steep faults formed in the basement and separation of the Adria Microplate occurred, characterized by carbonate facies with locally signifi cant volcaniclastic infl uence. A Late Triassic succession of Hauptdolomite and Dachstein limestones represents typical deposits of the huge isolated Southern Tethyan Megaplatform (VLAHOVIĆ et Figure 1: Shaded relief map of Croatia with superimposed area showing the recent distribution of Adriatic (Adriatic-Dinaric) Carbon- ate Platform (compiled from VLAHOVIĆ et al., 2005) and loca- tions of sampled Early Palaeogene bauxites. Border between the Adriatic and Dinaric units inferred (partly) after KORBAR, 2009. Geologia Croatica 55 Kovačević Galović et al.: Geochemical discrimination of Early Palaeogene bauxites in Croatia al., 2005). During the Late Liassic, it was dissected into smaller carbonate platforms, resulting in formation of the Adriatic Basin, with the Adriatic Carbonate Platform (AdCP) along its eastern side. This was marked by predominantly shallow-marine deposition, but a combination of synsedi- mentary tectonics and eustatic changes resulted in frequent emersions of variable duration, characterized by local depo- sition of bauxites. According to other authors (KORBAR, 2009, and references therein), two carbonate platforms (Adri- atic and Dinaric), separated by the inter-platform Budva-Cu- kali basin, were formed instead of the single AdCP. These were used as a basis for a new model of the Mesozoic–Ce- nozoic evolution of the region and further divided into four tectonostratigraphic units: Dinaridic NE unit (Inner Karst), Dinaridic SW unit (High Karst), Adriatic NE unit (Dalma- tian Karst) and Adriatic SW unit (Istrian Karst). Disintegra- tion of the platform(s) and the appearance of fl ysch basins began in the Late Cretaceous, while the transition from the Cretaceous to the Palaeogene was marked everywhere on the AdCP by a period of emersion. Intense tectonics contin- ued through the Palaeogene, with carbonate deposition on carbonate ramps, while tectonic contraction of the platform area during the Oligocene-Miocene resulted in the uplift of the Dinarides. One of the most distinctive features of the Di- narides is the widespread occurrence of ophiolites generated in subduction processes, fi rst in Dinaridic Tethys and later in the back-arc basin (PAMIĆ et al., 2002). The obducted ophiolites are predominantly peridotite tectonites, enriched in REE typical for ultramafi c rocks. Occurrences and deposits of bauxites can be found at sev- eral stratigraphic levels over the entire region of the Croatian Karst Dinarides – from Istria to Dalmatia (ŠINKOVEC & SAKAČ, 1981; SAKAČ et al., 1978; ŠEBEČIĆ et al., 1985; SAKAČ et al., 1984). Some (predominantly of Upper Eocene age from the Outer Dinarides), had large reserves of signifi - cant, economy-grade bauxite ore, but these are for the most part totally exhausted. Considering the whole formative pe- riod of the AdCP, the Palaeogene was particularly distinctive by a substantial shift of bauxite formation toward the more external zones of the External (Outer) Dinarides (ŠINKOVEC & SAKAČ, 1991). As a result, the majority of deposits formed between the Palaeocene and Upper Eocene, before the fi nal disintegration of the platform that culminated during the Oli- gocene-Miocene (VLAHOVIĆ et al., 2005). Before that, at the onset of the Tertiary period, Pc bauxites formed exten- sively over the low-lying, emerged SW part of the AdCP in- cluding Istria (Adriatic SW unit), Adriatic islands, and most of Dalmatian hinterland (Dinaridic SW unit) (KORBAR, 2009) occurring almost invariably in the form of small-size, economically often insignifi cant, ore bodies. 2.2. Field and analytical procedures 2.2.1. Sampling A total of 50 bauxite samples of Palaeocene age were collected from various sites (deposits and occurrences) in Istria (21), on the North Adriatic islands (12) including Krk, Cres, Rab, Goli and Pag, in Northern Dalmatia (8) and in Central Dalmatia (9). At all locations samples represent the bulk geochemical signa- ture of bauxites infi lling a single regional unconformity (Cre- taceous-Palaeogene transition), irrespective of particular hori- zons within the ore body (e.g. at the contact with the related palaeokarst), possibly with a different geochemical signal re- lated to issues of bauxite autochthony-allochthony or vadose- phreatic depositional-diagenetic environments (D’ARGENIO & MINDSZENTY, 1995; BARDOSSY, 1982). It is presup- posed here that multivariate analysis performed on the bulk geochemistry of a number of samples, can pinpoint the most important geochemical processes, by averaging all details down the vertical profi le. Detailed investigation at a single site ought to be performed later in order to screen geochemical and mineralogical data with particular reference to processes con- trolling the geochemical facies of bauxites in a specifi c part of the lithologic column. It must also be noted in passing, that all investigated bauxites are treated as being of Lower Paleogene (Pc) age, according to the age of the cover rocks, in spite of a possibility that some Istrian bauxites may have formed during more than one emergent stage due to a prolonged hiatus marked by non-deposition (ŠINKOVEC, 1973). 2.2.2. Sample preparation and analysis Fresh bauxite samples weighing about 3 kg in total were chipped and crushed by hand and fi nally split into fractions by quartering. Whole-rock samples were subsequently ground in a tungsten carbide pestle mortar mill (Retsch Lab Equip- ment) to pass through a <0.063 mm sieve to be prepared for the analytical work. Chemical analysis was performed at the ACME Ana- lytical Laboratories in Vancouver, Canada, using the Litho- geochemical Whole Rock Major and Trace Element analyt- ical method. Total abundances of the major oxides and several minor elements are reported on a 0.2g sample ana- lysed by ICP-emission spectrometry following a Lithium metaborate/tetraborate fusion and dilute nitric acid digestion. Total trace elements were analyzed by ICP-MS. Refractory elements underwent the same decomposition as the major elements (additional 0.2 g sample) while the rest are digested in hot Aqua Regia and analyzed by ICP Mass Spectrometry (0.5 g sample). Bauxite samples were analysed for a total of 32 elements including 10 major element (oxides): SiO2, Al2O3 Fe2O3, MgO, CaO, Na2O, K2O, TiO2, P2O5 and MnO; and 22 trace elements: As, Ba, Cd, Ce, Co, Cr, Cu, Ga, Hg, La, Mo, Nb, Ni, Pb, Sc, Sr, Th, U, V, Y, Zn and Zr. Mineralogical analysis was performed by X-ray diffrac- tion (XRD analysis) where the mineral composition of all samples was determined by the PANalytical X’Pert Powder diffractometer. The device is equipped with Ni-fi lter CuKα radiation, vertical goniometer with θ/θ geometry and PIXcel detector. Scan conditions were: 45kV and 40 mA, ¼ diver- gence slit and ½ antiscatter slits, step size 0.02° 2θ, time per step 2s. The sieved samples were then back-loaded on alu- minum holders, to ensure random mineral orientation. Pow- der diffraction data were collected in the range of 5-66° 2Θ. Mineralogical analysis was performed on four samples pre- pared in the same manner as for geochemical analysis. Only one sample representative of each single group was selected for the purpose. Selection was based on the mean value of Geologia Croatica 56 Geologia Croatica 65/1 the major-element compositions so that the least value of the Squared Mahalanobis Distance (SMD) for each group (the least distance from the group centroid), was used as a crite- rion. Mineralogical analysis was obtained by XRD on the bulk samples (IPC-7, KRK-4, DR-11, and IMPC-1). The fol- lowing mineral compositions were determined: boehmite, haematite, goethite and anatase in samples DR11, IMPC1 and KRK4. Sample IPC7 is different because it contains gibbsite which doesn’t appear in other samples. Boehmite is a dominant mineral phase in the 3 samples, while haematite, goethite and anatase appear in minor amounts. Boehmite was determined by the diffractions maximums on d=6.10, 3.16, 2.34 and 1.86 Å. Haematite has its characteristic peaks on d=3.68, 2.69, 2.51 and 1.69 Å. Goethite has diffraction max- imums on d=4.16, 2.69 and 2.45 Å. Anatase was identifi ed by peaks d=3.51, 2.37 and 1.66 Å. Gibbsite appears only in sample IPC7 and was determined by strong refl ection peaks on d=4.84, 4.37 and 3.31 Å. 3. STATISTICAL CONSIDERATIONS 3.1. The data A set of 32 elements including 10 major and 22 trace elements was selected as predictor variables in building the original discriminant model. Summary statistics for the whole dataset prior to the multivariate statistical procedure are displayed in Table 1 (minimum, maximum, median, mean, standard de- viation and skewness). Since most of the variables are char- acterized by non-normal, positively skewed, frequency dis- tributions (except Al2O3 and TiO2, Ga, Nb, Th and Zr which are negatively skewed), appropriate transformations were found necessary to acquire a more symmetric distribution. As a general rule, most geochemical data do not follow normal (neither lognormal) distribution (e.g. MATSCHULLAT et al. 2000; REIMANN & FILZMOSER, 2000; REIMANN et al. 2005); a problem arising from complex non-linear dynamics, feedbacks and thresholds within a natural system character- ized by the particular suite of variables (e.g. HUGGET 1998; PHILLIPS, 1999). Univariate distributions of the input data were examined by the Shapiro-Wilks W test of normality (added to Table 1 as p-values before and after normalization). Conventional normalization procedure using log-transforma- tions was subsequently applied where necessary to stabilize the variance of the original data. This process included all the major elements except P2O5, and a greater part of the trace elements exclusive of Ga, La, Nb, Sc, Th and Zr which are normally distributed (all marked by the asterisk). According to the applied test, 17 more variables attained normal distri- bution after normalization (SiO2, Fe2O3, MgO, CaO, As, Ba, Cd, Ce, Co, Cu, Hg, Mo, Pb, Sr, V, Y and Zn (p>0.05, marked by double asterisk)). However, where the normalization pro- cedure failed, having produced an even greater skew with respect to the original distribution (such as with Al2O3 and Na2O), the data were rather left untransformed. As with all multivariate statistical procedures, yet another assumption had to be made before DFA can be successfully utilized in research – that of suffi cient sample size supplying enough information upon which to found analysis. Based on the va- riety of general recommendations considering the importance of sample size and sample-to-size ratio reviewed in a number of works (e.g. ARRINDEL & van der ENDE, 1985) 50 ob- servations was deemed suffi cient but major and trace ele- ments were analyzed as separate data matrices. 3.2. Building a discriminant function model (DFM) Multiple (multi-group) discrimination analysis (MDA) is a statistical technique that is particularly useful when applied to distinguish between several pre-defi ned groups based on a great number of observations. Its purpose, defi ned in a sta- tistical sense, is to maximize the between-group variance in comparison to the variance within each group (e.g. DILLON & GOLDSTEIN, 1984). In the process, a hypothesis is tested that all observed groups have the same multivariate mean against the alternative that at least one multivariate mean is different (ROCK, 1988). Provided that alternative hypoth- esis is accepted (which does not mean that each pair of groups must necessarily be plainly separated and distinct), the orig- inal set of data is then recalculated by MDA into a number of discriminant scores, allocating each object or group (the latter represented by its mean), along one or more lines – linear discriminant functions (e.g. KRUMBEIN & GREY- BILL, 1965; DOORNKAMP & KING, 1971; DAVIS, 1986). In this way the multivariate problem simply collapses into a fewer-dimension solution, one less than the number of groups (K-1), or equal to the number of variables (p), which- ever is the smaller. Here, discriminant analysis from the statistical software package of STATISTICA, Release 7.1 (StatSoft, Inc., 2006) was used to investigate chemical differences between the four groups of bauxites separated previously by independent criteria such as their geographical position and palaeotec- tonic settings within the AdCP as a major geotectonic unit. The groups containing 50 samples were determined as Early Palaeogene (Palaeocene) bauxites and sampled from differ- ent quarters of the AdCP, namely Istria (IST), North-Adriatic Islands (NAI), North Dalmatia (NDA), and Central Dalma- tia (CDA), roughly following the position of the formerly established tectonostratigraphic units (KORBAR, 2009). In order to achieve the best separation between groups and ex- plain the geological causes underlying the structure of input data, two discriminant models were constructed based on the two sets of predictor variables, namely the bulk concentra- tions of major (10) and trace elements (22). 4. RESULTS AND DISCUSSION The results of the MDA are briefl y summarized in the joint table (Tab. 2) comprising both research models containing major and trace elements. The overall signifi cance of their discrimination is tested by the appropriate multivariate tests (Tab. 3) showing the extremely low associated probabilities (p<0.000) in both cases, which is required to safely proceed with computing discriminant functions (DFs). Since the same number of groups (K=4) is studied in both models, the between-group variation is completely explained by the three DFs (K-1). Table 2 reveals that in both models, DF1 explains Geologia Croatica 57 Kovačević Galović et al.: Geochemical discrimination of Early Palaeogene bauxites in Croatia the largest portion of the total variability hidden within the original main- and trace elements data spread, amounting to almost 80% for the latter. Note, however, that in the trace- element DFM the third function (DF3) exhibits a low con- tribution to the total variance, which can be seen both by the tested signifi cance (p=0.146) and low eigenvalues (Tab. 2), meaning that only the fi rst two DFs are suffi cient to separate the four bauxite groups based on their trace element content. 4.1. Functional models (Labeling discriminant space) Labelling DFs is an essential part of the analysis since it offers a geologically meaningful interpretation to the whole discrimi- nation scheme. Through this process the hidden mathematical Table 1: Descriptive statistics. Element Min Mean Med Max StDev Skew S–W(p) S–W(p1) SiO2 (%) 1.02 3.914 3.415 9.10 2.059 0.825 0.004 **0.560 Al2O3 (%) 34.50 50.114 50.415 58.58 5.308 -0.890 0.021 – Fe2O3 (%) 14.76 26.114 25.955 45.96 5.294 0.993 0.027 **0.750 MgO (%) 0.06 0.137 0.11 0.49 0.077 2.388 0 **0.070 CaO (%) 0.04 0.126 0.115 0.64 0.094 3.525 0 **0.116 Na2O (%) 0.005 0.02 0.01 0.33 0.046 6.664 0 – K2O (%) 0.005 0.046 0.03 0.20 0.047 1.761 0 0.012 TiO2 (%) 1.60 2.889 2.955 3.88 0.493 –0.699 0.030 0.030 P2O5 (%) 0.005 0.054 0.053 0.113 0.025 0.046 *0.608 – MnO (%) 0.02 0.079 0.05 0.46 0.083 3.256 0 0.013 As (mg/kg) 1.7 39.198 36.15 154.9 32.304 1.844 0 **0.132 Ba (mg/kg) 6.0 26.280 24.0 73.0 13.028 1.749 0 **0.117 Cd (mg/kg) 0.1 2.03 1.2 11.0 2.438 2.250 0 **0.567 Ce (mg/kg) 64.6 233.218 193.8 645.3 130.050 1.321 0 **0.825 Co (mg/kg) 14.2 41.33 38.2 91.9 16.866 1.070 0.004 **0.985 Cr (mg/kg) 362.76 713.07 578.37 1423.62 309.056 0.835 0 0.003 Cu (mg/kg) 21.9 102.672 82.3 250.5 60.749 1.087 0 **0.503 Ga (mg/kg) 33.6 53.024 53.55 65.1 7.309 -0.662 *0.104 – Hg (mg/kg) 0.03 0.314 0.225 1.02 0.256 1.135 0 **0.189 La (mg/kg) 40.7 99.106 93.8 179.3 31.209 0.386 *0.141 – Mo (mg/kg) 0.9 9.89 7.55 33.0 7.961 1.125 0 **0.237 Nb (mg/kg) 30.7 57.278 59.4 75.4 9.154 –0.774 *0.057 – Ni (mg/kg) 88.0 256.76 224.5 1092.0 178.974 3.094 0 0.003 Pb (mg/kg) 44.2 103.018 97.6 196.6 33.985 0.828 0.030 **0.842 Sc (mg/kg) 35.0 57.5 54.0 91.0 13.239 0.624 *0.096 – Sr (mg/kg) 27.6 81.728 74.7 220.4 36.582 1.489 0 **0.240 Th (mg/kg) 28.5 45.704 45.25 60.7 6.351 –0.224 *0.496 – U (mg/kg) 4.6 9.076 8.7 26.9 3.565 2.834 0 0.025 V (mg/kg) 286.0 622.24 539.0 1876.0 312.099 1.938 0 **0.064 Y (mg/kg) 31.4 85.392 69.7 255.9 45.305 2.163 0 **0.072 Zn (mg/kg) 12.0 125.180 90.0 422.0 92.700 1.090 0 **0.340 Zr (mg/kg) 312.3 530.06 532.55 721.2 81.161 -0.611 *0.116 – Table 2: Tests of residual roots (discriminant functions) for both DFMs. DF Eigen value Eigen (%) Canon. R Wilks �� chi2 df p- level Major-element DFM 1 2.385 56.93 0.839 0.082 104.9 30 0.000 2 1.067 25.46 0.718 0.278 53.7 18 0.000 3 0.737 17.61 0.651 0.576 23.2 8 0.003 Trace-element DFM 1 24.283 79.42 0.980 0.003 208.6 66 0.000 2 5.199 17.00 0.916 0.077 92.3 42 0.000 3 1.094 3.58 0.723 0.477 26.6 20 0.146 Geologia Croatica 58 Geologia Croatica 65/1 structure underlying the raw geochemical observations can be easily exposed to the observer. Discriminant loadings (simple correlations of variables with respective DFs), or structure co- effi cients, are particularly useful in clarifying the individual contribution of each descriptor variable (major and trace ele- ments), to the overall discrimination. In this sense the variables with small discriminant loadings which contribute little to the explanatory power of DFs in both DFM are seen as irrelevant and can be eliminated from further consideration. This is easi ly seen on the variable diagrams that provide the quickest and most informative insight into the structure of discriminant space, suggesting also which subset of variables (descriptors) most clearly separates the a priori defi ned groups (Figs. 2a, 3a and 5a). Obviously, elements clustered more or less tightly around the intersection of discriminant axes such as SiO2, Fe2O3 and Na2O in major-element DFM, and the majority of elements in trace-element DFM excluding Cr, V, As, Ga and some others, do not form the best subset required for mean- ingful interpretation of DFs in terms of geological processes. Association among descriptor variables and related groups is best represented geometrically, viewing the DFs as orthogonal axes intersecting in the reduced discriminant space. However, it is not possible to compare the variable and group scatterplots directly, since different scales are used in each case. The scatterplots of variable loadings (Figs. 2a, 3a and 5a) display discriminant axes as normalized vectors, while the scatterplots of canonical means (group centroids), and individual objects (samples), display discriminant score vectors (Figs. 2b, 3b and 5b). Thus, reciprocity between the variables and groups should always be considered using their shared position along the appropriate axis. 4.1.1. Major-element model In the major-element model, all three DFs are highly signif- icant with DF1 explaining considerably over half of the total variation (57%) between the groups (Tab. 2). As seen from the scatterplot of variable loadings (Fig. 2a), DF1 is slightly bipolar, primarily separating the Istrian group of Palaeocene bauxites (IST), from both the Central Dalmatian (CDA) and North Dalmatian (NDA) groups, while bauxites from the North-Adriatic islands (NAI) remain largely undistinguished (Fig. 2b). The rationale for this separation is founded in the negative association between the K2O–TiO2 variable set on the one side and P2O5 on the other. Geochemically, it can be understood as IST bauxites being enriched in K2O–TiO2 and depleted in P2O5 with regards to NDA and CDA bauxites, and vice versa. Although the overlap is considerable between all groups, a distinct change in content of respective elements can be easily detected if groups are placed in the appropriate palaeogeographic/palaeotectonic setting over the investi- gated part of AdCP. Four bauxite groups are regularly scat- tered in the IST-NAI-NDA-CDA succession following the NW-SE strike of the Upper Cretaceous-Paleogene boundary (except in Istria where hanging-wall sediments were com- pletely removed). A small but regular decrease in the K2O– TiO2 association is easily observable from Istria towards Central Dalmatia (from right to left on the sample-centroid scatterplot, Fig. 2b). Thus, the geological interpretation of DF1 can be established on the “enrichment-depletion” rela- tionship of K2O–TiO2/P2O5 variable opposites with reference to their specifi c palaeotectonic setting within the AdCP. It must be noted, however, that the central position of the NAI bauxites, close to the main centroid and overlapping both IST and CDA bauxites, indicates the average major-element composition of a “transitory” group. A general decrease in the K2O–TiO2 content in Palaeocene (Pc) bauxites in a NW- SE direction, from Istria to Dalmatia, can be associated with differing palaeographical conditions at various parts of the Figure 2: Comparison between variables and groups in the major-element DFM: scatterplots of (a) variable loadings and (b) individual objects (sam- ples) in reduced discriminant space of the fi rst two discriminant functions (DF1-DF2). Table 3: Multivariate test for overall signifi cance of discrimination. Major-element DFM Trace-element DFM No. of variables 10 22 Wilks lambda 0.082 0.003 Approximate F ratio 4.888 6.818 Degrees of freedom [30; 109] [66; 75] p-level p < 0.000 p < 0.000 Geologia Croatica 59 Kovačević Galović et al.: Geochemical discrimination of Early Palaeogene bauxites in Croatia AdCP since the Cretaceous-Paleogene transition (VLAHOVIĆ et al., 2005; KORBAR, 2009). Geodynamic evolution of the External Dinarides in post-Mesozoic times may have caused a prolonged exposure of primary bauxites, accounting for recurrent contamination by airborne (aeolian dust or volca- nic ash), or terrigenous (fl uvial) sedimentary material. Due to the extended hiatus lasting in parts of Istria from the Early Cretaceous (shallow-water carbonates) to the Early Eocene (foraminiferal limestones) (KORBAR, 2009, and references therein) Istrian bauxites (IST) may have been graded and degraded repeatedly due to the input of new material and changing environmental conditions (e.g. discontinued leach- ing as a result of changing climate or drainage conditions), and thus never deprived completely of clayey (particularly illitic) material. This reworking is advocated by the miner- alogical (XRD) analysis showing that only the bauxites from the SE part of the Dinaridic SW unit (CDA) contain gibbsite (hydrargillite), which is the constituent part of the primary bauxites, while other investigated groups (IST+NAI+NDA) are boehmitic (Fig. 4). Since the primary (gibbsitic) karst bauxites are rarely preserved in the Mediterranean area (HOSE, 1986), the dehydration of gibbsite into boehmite as an end-product of intensive aluminosilicate weathering in a subtropical environment (palaeosols and recent soils of trop- ical and subtropical areas) with potentially high leaching rates (HERRMANN et al., 2007; D’ARGENIO & MIND- SZENTY, 1995; KLEBER et al., 2007) must have been a common process in the most parts of the AdCP during the Cretaceous-Palaeogene transition. However, Pc bauxites from the Imotski area (CDA) are predominantly gibbsitic (Fig. 4; Tab. 4) indicating prevalently hydrous conditions (intense leaching due to intense rainfall and rapid drainage, CHORLEY et al., 1985) during most of the relatively short emersion stage. Mineralogical analysis also demonstrates the absence of anatase as a dominant TiO2 polymorph usu- ally present in other groups. The low content of TiO2 is char- acteristic of the CDA group while being abundant in the IST and NAI (up to 3.88 % in KRK-2 sample) together with K2O (Fig 2a, b), meaning that at least a portion of the TiO2 com- ponent must have been enriched by reworking primary baux- ites after being formed as fi ne-grained anatase as a result of weathering of the titanium-bearing silicates, similar to recent regoliths (FORCE, 1991). Conversely, most of the P2O5 can be co-precipitated with Fe-Mn oxy-hydroxides (goethite) un- der oxidative conditions. It is well known that phosphate ad- sorption by goethite and other Fe oxides strongly infl uence its concentrations in soils and aquatic environments (TOR- RENT et al., 1992). This interaction must also have been important in controlling phosphate in the bauxite-forming palaeoenvironment. Although DF1 is generally neutral with regards to Fe2O3, the P2O5 content is loosely associated with MnO at the negative pole of the function, indicating the pos- sible scavenging role of Mn-oxyhydroxides as a proxy chan- nel for phosphorus accumulation in CDA bauxites. However, an even closer association of the CaO component with P2O5 points to apatite as the main phosphorus phase (Fig. 2a). Apatite is a widespread accessory phase in the magmatic se- quence of ophiolite complexes and is widely documented in literature describing the Ni-Cr-rich ophiolite-derived later- ites of Northern Greece (e.g. ECONOMOU-ELIOPOULOS, 2003). Not suprisingly, perhaps, the lowest P2O5 concentra- tions are observed in IST bauxites at the westernmost part of the AdCP (commonly below 0.01%; 0.04% in average) far from the Dinaridic Ophiolite Zone. Alternatively, high values can be found in all groups (up to 0.11% in NDA or 0.10% in NAI) indicating that removal of P2O5, more than enrichment was typical for the bauxite-forming environment, being most effective over the Istrian Peninsula. It is evident from above that DF1 can be functionally explained from the perspective of changing environmental Figure 3: Comparison between variables and groups in the major-element DFM: scatterplots of (c) variable loadings and (d) individual objects (sam- ples) in reduced discriminant space of the fi rst and third discriminant func- tions (DF1-DF3). Table 4: Qualitative mineral composition of the main components in Pc bauxites. Sample Mineral content DR–11 boehmite, haematite, goethite, anatase IMPC–1 gibbsite, haematite, goethite IPC–7 boehmite, haematite, goethite, anatase KRK–4 boehmite, haematite, goethite, anatase Geologia Croatica 60 Geologia Croatica 65/1 (palaeogeographical) conditions prevailing during the AdCP Cretaceous-Paleogene emergent phase which resulted in a particular “enrichment-depletion” major-element signature. Although statistically highly signifi cant in the major- element model, the other two discriminant functions DF2 and DF3 explain a smaller fraction of the total variation (25.5 and 17.6 %, respectively), adding some new insight into the geochemical interpretation of the all-important DF1. Clari- fi cation of DF2 revolves primarily about separating the two “inner” groups among the palaeogeographically established IST→CDA sequence within the AdCP. Although not easily observed from the group scatterplot (Fig. 2b) it is essential that the “end groups” in this succession (IST vs. CDA) do not lose their members to each other (Tab. 5). However, DF2 separates between NAI and NDA with extremely high effi - ciency in that only one in 20 bauxite samples is lost to other group (NDA to NAI). Discrimination between NDA and NAI is based on the polarity relationship between the MnO– (CaO–Fe2O3)/MgO major-element suite, which is possibly a refl ection of palaeodynamic and palaeoclimatic conditions prevailing in the central portion of the investigated bauxite- bearing Croatian high karst area (External Dinarides) during the Cretaceous-Palaeogene transition. The recent hinterland part of the AdCP (NDA bauxites), can be seen as an ancient repository for the hydrothermally derived marine manganese input from the pelagic realms caused primarily by tectonic/ eustatic changes (CORBIN et al., 2000, and references the- rein). In this context the higher manganese content would correspond to a transgressive maximum, whereas the lower content to a regressive maximum. According to CHESTER (1990), almost 90% of continental Mn is trapped within coastal and estuarine environments, accounting for periodic ingress of marine waters into terrestrial and lacustrine sys- tems of very low plate-interior relief (D’ARGENIO & MINDSZENTY, 1995). This would explain the elevated con- tent of MnO (with Fe2O3 and CaO) in NDA bauxites having occurred immediately before or during the fi nal subsidence of emergent platform areas and subsequent diagenesis of buried bauxite (Fe-Mn oxy-hydroxides precipitated in oxy- gen-rich waters). In contrast, the increased content of MgO in NAI bauxites may indicate an indurate subaerial setting, characterized by an interim shift to more arid conditions, with limited percolation of meteoric waters in primary baux- ites, which results in ineffi cient removal of Mg ions and for- mation of Mg-rich clays (KETZER et al., 2003), indicated by an MgO–(TiO2–Al2O3), as opposed to a MnO–(CaO– Fe2O3) major-element signature, although other scenarios for relative Mg-enrichment are possible. The third discriminant function DF3 (Figs. 3a, b) is es- sentially monopolar, and it highlights a specifi c major-ele- Figure 4: X-ray diff ractograms of four Early Palaeogene bauxite samples from the Croatian part of the AdCP. Geologia Croatica 61 Kovačević Galović et al.: Geochemical discrimination of Early Palaeogene bauxites in Croatia ment pattern which is largely concerned with separation of aluminum (Al2O3) and titanium oxides (TiO2), from the suite of elements including the clayey component from the rest (K2O–SiO2–MgO–Na2O). Accordingly, DF3 separates basi- cally on the ground of the clay content in bauxites, with vari- ations (MnO, Fe2O3), explained earlier as the degree of leach- ing effi ciency and hydrolysis, and relates most particularly to the CDA bauxites. It is thus a supplement to DF1, but re- veals a distinct gap within the single group dividing most of its members from the primary IST-NAI-NDA-CDA sequence. This separation refers to specifi c conditions in a part of CDA bauxitiferous environment distinguished by sluggish removal of leachates, probably due to low amounts of free percolation in waterlogged situations and the occurrence of montmoril- lonite, illite and chlorite as the resulting clay products (CHOR- LEY et al., 1985). It must be noted that DF3 also reveals some intrinsic heterogeneity within the IST group which probably can be ascribed to changing palaeogeographic and palaeocli- matic changes during the long hiatus, having affected the northernmost portion of AdCP. This refers most to IPC-14 where the bauxites, after being reworked, have never been completely leached out (K2O and other clay constituents) but must have undergone conditions of impeded drainage due to periodic rising of the water table (swamps). 4.1.2. Trace-element model Unlike the major-element DFM only two DFs are statisti- cally signifi cant in the trace-element DFM (Tab. 2), of which DF1 accounts for almost 80% of the variation between the groups. This model is a clear-cut example of how individual objects can be unambiguously assigned into their a priori defi ned groups (Figs. 5a, b). The classifi cation effi ciency is 100%, implying total separation between the four investi- gated groups of bauxites (Tab. 5). This is strongly opposed to the major-element DFM where group division is some- what blurred, in spite of the same criterion applied in dis- crimination. The group assignment details based on the Squared Mahalanobis Distance (SMD), also show that dis- tances between the groups are considerably larger than in the major-element DFM (Tab. 6), with a difference that NDA is placed further away from IST (IST/NDA = 120.72), than CDA (IST/CDA = 111.31), modifying the mathematically defi ned geochemical-(palaeo)geographical distance pattern found between the groups in the major-element DFM. Com- Table 5: Classifi cation matrix. PREDICTED GROUPS Major-element DFM Trace-element DFM OBSERVED GROUPS IST NAI NDA CDA Total % correct IST NAI NDA CDA Total % correct IST 19 1 1 0 21 90.48 21 0 0 0 21 100.0 NAI 2 10 0 0 12 83.33 0 12 0 0 12 100.0 NDA 0 1 7 0 8 87.50 0 0 8 0 8 100.0 CDA 0 1 1 7 9 77.78 0 0 0 9 9 100.0 Total 21 13 9 7 50 86.00 21 12 8 9 50 100.0 Table 6: Squared Mahalanobis Distance (SMD). Major-element DFM Trace-element DFM GROUP IST NAI NDA CDA IST NAI NDA CDA IST 0.00 0.00 NAI 7.54 0.00 18.64 0.00 NDA 11.13 10.54 0.00 120.72 94.14 0.00 CDA 15.94 10.31 10.11 0.00 111.31 117.54 35.83 0.00 Figure 5: Comparison between variables and groups in the trace-element DFM: scatterplots of variable loadings (a) and individual objects (samples) (b) in reduced discriminant space of the fi rst two discriminant functions (DF1-DF2). Geologia Croatica 62 Geologia Croatica 65/1 plete/incomplete separation between groups based on the major-element/trace-element signature was observed earlier in similar investigations (PEH & HALAMIĆ, 2010), and can be explained on the grounds that major elements enter vari- ous processes active during the sedimentary cycle (from weathering to burial and diagenesis), while accumulation or depletion of trace elements usually narrows the scope of re- search to some particular segment of the cycle. DF1 is essentially a monopolar function and it can be interpreted geochemically as refl ecting a particular position of Cr against a number of trace elements with low discrimi- natory potential, clustered around the main centroid. Chro- mium is typically enriched in ultramafi c and mafi c rocks to- gether with Ni although the latter is not so prominent in the analyzed bauxites (Fig. 5a). Elevated values of Cr in baux- ites can be indicative of ophiolitic complexes containing ul- tramafi cs and related rocks as a parent material, particularly given its very low mobility even in strongly-weathered en- vironments, but especially under moderately oxidizing and reducing conditions and near-neutral pH values (De VOS et al., 2006). Together with other trace elements such as Ti and Zr in particular, which are considered immobile during weath- ering and hydrothermal alteration processes (MACLEAN & BARRET, 1993), the ratios Cr forms in bauxites do not differ greatly from those in parent rocks (VALETON et al., 1987) and thus can be applied in bivariate or ternary diagrams for determination of the parent material. It is clear from the dia- grams (Figs. 5a, b) that a clear-cut split between the group pairs caused by Cr-enrichment in NDA and CDA bauxites from the central and SE parts of the investigated AdCP (High Karst Dinaridic unit), must suggest an extraneous source of chromium – most probably the Dinaridic ophiolite belt with large ultramafi c massif and radiolarite formation (PAMIĆ et al., 2002) at the AdCP NE border as its host rocks. In con- trast, IST and NAI bauxite groups of the Istrian Karst Adri- atic unit and northern part of the High Karst Dinaridic unit, respectively, contain below-average Cr content. Typically, Cr-content amounts to 1232 mg/kg in NDA or even up to 1424 mg/kg in CDA with mean values of 1053 mg/kg and 1142 mg/kg, respectively. This enrichment is considerably higher than that for the majority of Mediterranean karst baux- ites of various stratigraphic positions including the Upper Palaeogene (Eocene) bauxites from the Obrovac area (CAL- AGARI & ABEDINI, 2007). Conversely, IST bauxites con- tain only 489 mg/kg of Cr on average while NAI bauxites are slightly more enriched; 556 mg/kg indicating a com- pletely different (felsic) lithological provenance. Indica- tively, modern soils from North and Central Dalmatia are highly enriched in chromium (up to 444 mg/kg, Obrovac area), being most possibly contaminated by the nearby baux- ite deposits, albeit mostly of Eocene age, abounding in the area (HALAMIĆ & MIKO, 2009). Determination of the pos- sible precursor rock type can be easily deduced from the ter- nary diagram comparing the Cr, Zr and Ga concentration values of Palaeocene bauxites formed on the AdCP (Fig. 6). If compared to corresponding trace-element DFM scatter- plots (Figs. 5a, b), a striking shift of NDA and CDA groups to the mafi c and ultramafi c fi eld is obvious drawing these bauxites near to those in bordering Bosnia and Herzegovina, or even farther east in Greece (ÖZLÜ, 2004; CALAGARI & ABEDINI, 2007, and references therein). Apart from chromium, DF1 is characterized by small- scale variations in the content of other trace elements and only their relative position with respect to the main centroid indicates slightly elevated concentrations of V, Cd and Pb (as well as slightly decreased concentration of As, Hg and others) in CDA and NDA groups with respect to IST and NAI groups, and vice versa. The second discriminant function DF2 is slightly bipo- lar and contains considerably lower explanatory potential with respect to DF1 (only 17%). It is marked by a negative association between As and the suite of trace elements in- cluding Ga, Zr and possibly Nb. However, this relationship calls for caution due to commonly weak variable loadings which renders its geological interpretation rather specula- tive. An inverse relationship between the two trace-element assemblages could be interpreted as representing differing conditions relating to provenance, weathering and deposi- tion during the early stages of bauxite formation, which strongly affect their chemical behaviour. Since genesis of primary bauxites in many facets resembles the formation of red claystone and terra rossa soils after the subsequent pedo- genesis (MERINO & BANERJEE, 2008), it is possible to treat their trace element geochemistry in a similar way as in palaeosols, whether related to weathering intensity, evalua- tion of leaching, or provenance (SHELDON, 2009). Ele- ments of interest in this context are undoubtedly Zr and Nb which are characteristically relatively immobile during Figure 6: Ternary diagram for Zr, Cr and Ga concentrations in the samples of the four investigated groups of Early Palaeogene bauxites in Croatia; the numbered circles represent the area of infl uence of felsic (1), inter- mediate (2), mafi c (3) and ultramafi c (4) rocks indicated as probable parent material in genesis of the Mediterranean karst bauxites (after ÖZLÜ, 1983); UCC = average Zr-Cr-Ga content in the upper continental crust (after TAYLOR & MCLENNAN, 1985). Geologia Croatica 63 Kovačević Galović et al.: Geochemical discrimination of Early Palaeogene bauxites in Croatia weathering of source rocks and bauxite genesis, including Ga which is typically related to Al and processes of intense leaching, linked with supergene (surface or near-surface) en- vironment under tropical and subtropical climates (HIERO- NYMUS et al., 2001). As DF2 clearly discriminates between the NDA-NAI group pair set apart by a prominent Ga-Zr-Nb association, and a CDA-IST pair characterized by As (Figs. 5a, b), this relationship can possibly highlight the redox con- ditions controlling the trace-element enrichment-depletion in the bauxite-bearing palaeo-environment. Arsenic accumu- lation in subaerially formed sedimentary rocks is most often recognized through the process of sorption on Fe oxy-hydrox- ides, which are precipitated in the form of ooids (goethite) slowly formed under mainly oxic conditions (BANNING & RÜDE, 2010). However, lacking precise XRD analysis, the origin of As is ambivalent in spite of possible signifi cant As- Fe correlation since a variety of processes in the reduced en- vironment may induce co-precipitation of As with Fe sulfi des. It is widely believed that sulfi dogenesis via microbial SO4 -2 reduction can slow down As mobility in reducing subsurface environments (BURTON et al., 2011). Thus, at least a portion of the As accumulated particularly in Istrian bauxites can de- rive its origin due to precipitation of Fe-sulfi de minerals such as pyrite. The presence of sedimentary pyrite in bauxites from Minjera (Istria) (ŠINKOVEC et al., 1994) strongly advocates this possibility. Alternatively, As hosted in CDA bauxites in- dicates a different origin, since sulfi des generally do not func- tion as an important sink for lithophile elements such as Cr (HUERTA-DIAZ AND MORSE, 1992) which abound in CDA bauxites. Most probably, it is present via the Fe-oxyhy- droxides (haematite, goethite) derived from the Dinaridic ophiolite complex for which As enrichment is well-docu- mented (e.g. in radiolarian cherts, PEH & HALAMIĆ, 2010). Conversely, Nb, Zr, and Ga in particular, would indicate hydrous conditions where bases were effectively leached in primary bauxites. That Ga is strongly associated with Al in this process can be easily deduced by the trace- and major- element DFM comparison (Fig. 3a vs. Fig. 5a) which both separate the Al-Ga higher-content NAI and NDA from lower- content IST and CDA groups. However, an obvious mis- match between the diagrams caused by better separation per- formed by the trace-element DFM may indicate that Al and Ga (including Zr and Nb) do not necessarily follow the same paths controlled by the physico-chemical conditions of the bauxite-bearing environment in all parts of the AdCP. It usu- ally calls for reworking the primary (gibbsitic) bauxites since the tight association between Al and Ga may be disturbed, or even reversed, if gibbsite previously formed by lateriza- tion (bauxitization) is later dissolved due to the aforemen- tioned environmental changes. Ga, which is more soluble, tends to be leached out, while Al migrates downward and precipitates again as gibbsite (HIERONYMUS et al., 2009). This was the probable scenario for distinctive absence of Ga (Nb, Zr) in IST and CDA bauxites, although Al is enriched only in rare samples of these groups (in the form of gibbsite in CDA or boehmite in IST bauxites). 5. CONCLUDING REMARKS Two DFMs were built in this study in order to distinguish geochemically between the four groups of Pc bauxites sam- pled from the various corners of the Croatian part of the AdCP. The bauxites, having derived from the same regional unconformity, were assumed to have undergone generally similar conditions of formation with regards to global (eu- stasy and climate), and regional (volcanism and tectonics) controls during the subaerial exposure of the platform. How- ever, the local portions of emergent palaeoenvironment may have easily experienced a slightly different recombination of controlling factors causing variations in depositional and diagenetic facies (most particularly with regards to the amount of free percolation in the weathering mass), and nec- essarily variable resulting geochemical signature. High per- formance of separation between the a priori defi ned groups of bauxites achieved by MDA, especially consulting the trace-element DFM, demonstrated a high degree of effi cacy in characterizing specifi c environmental conditions that lead to formation and emplacement of bauxites onto the carbon- ate platform. Important results of MDA analysis can be briefl y sum- marized as follows: – Almost complete separation between the four groups of Pc bauxites from various parts of AdCP (from Istria to the Central Dalmatia) is attained by MDA using the geochem- ical major- and trace-element data array. – The major-element DFM demonstrates a lower degree of separation between groups (86 %) with respect to the trace- element DFM owing to the fact that major elements par- ticipate in a variety of processes during the sedimentary cycle resulting in the necessary overlap in the a priori nat- urally defi ned groups. Typically, the best discrimination between the groups is achieved on DF1, extracting more than a half of the total variability (57 %) via the bipolar K2O/P2O5 “enrichment-depletion” relationship. This pat- tern can be identifi ed as signaling the multiple reworking of proto-bauxitic material in changing environmental con- ditions prevailing during the AdCP Cretaceous-Palaeogene emergent phase. Spatially, it is manifested in regular geo- graphical IST-NAI-NDA-CDA succession showing grad- ual K2O decrease (P2O5 increase) in a SE direction. The functions DF2 and DF3 are of minor importance expound- ing tectonic/eustatic controls over periodic ingress of ma- rine waters onto the carbonate mainland (MnO, NDA) or long-lasting subaerial exposure (MgO; NAI), and overall degree of maturity characterized by the presence/absence of clay material (enriched Al2O3 and TiO2 components in majority of groups except for some CDA and IST samples), respectively. – Trace-element DFM is more suitable for both discriminat- ing and identifying purposes since the classifi cation effi - ciency of the established predictive model is the highest possible (100%). Discrimination is unequivocally based on Cr content which separates the CDA-NDA (Cr-en- riched) from the NAI-IST group pair, accounting for al- most 80% of the explanation potential of DF1. This most Geologia Croatica 64 Geologia Croatica 65/1 probably refers to the provenance issues relating the source material of CDA-NDA bauxites to the mafi c precursor rocks from the adjacent Dinaridic ophiolite belt. Labeling DF2 is speculative due to low discriminant loadings but it possibly highlights the redox conditions controlling the trace-element enrichment-depletion in the bauxite-bearing palaeo-environment. ACKNOWLEDGMENT This study was supported by The Ministry of Science, Educa- tion and Sports, Republic of Croatia (MZOŠ) – Scientifi c Proj- ect: The Map of Mineral Resources of the Republic of Croatia. Their support is greatly appreciated. The authors are thankful to all who contributed to the execution of this research. A spe- cial word of thanks is due Tvrtko KORBAR and Miron KO- VAČIĆ who provided us with additional bauxite samples pur- suing their own fi eld work within the scope of other MZOŠ scientifi c projects related to the Adriatic (Adriatic–Dinaric) carbonate platform. Finally, this manuscript was greatly im- proved by the suggestions and the commentaries offered by the reviewers to whom we are deeply indebted. REFERENCES ARRINDELL, W.A. & VAN DER ENDE., J. (1985): An empirical test of the utility of the observations-to-variables ratio in factor and components analysis.– Appl. Psych. Meas., 9, 165–178. doi:10.1177/ 014662168500900205 BANNING, A. & RÜDE, T.R. (2010): Enrichment processes of arsenic in oxidic sedimentary rocks - from geochemical and genetic cha- racterization to potential mobility.– Water Res., 44, 5512–5531. doi:10.1016/j.watres.2010.05.034 BARDOSSY, G. (1982): Karst bauxites: bauxite deposits on carbonate rocks.– Akadémiai Kiadó, Budapest, 441 p. BURTON, E.D., JOHNSTON, S.G. & BUSH, R.T. (2011): Microbial sulfi dogenesis in ferrihydrite-rich environments: Effects on iron mineralogy and arsenic mobility.– Geochim. Cosmochim. Ac., 75, 3072–3087. doi:10.1016/j.gca.2011.03.001 CALAGARI, A.A. & ABEDINI, A. (2007): Geochemical investigations on Permo-Triassic bauxite horizon at Kanisheeteh, east of Bukan, West-Azarbaidjan, Iran.– J. Geochem. Explor., 94, 1–18. doi:10.1016/ j.gexplo.2007.04.003 CHESTER, R. (1990): Marine Geochemistry.– Unwin Hyman, Lon- don, 689 p. CHORLEY, R.J., SCHUMM, S.A. & SUGDEN, D.E. (1985): Encyclo- pedia of Geomorphology.– Routledge Publishing, 648 p. CORBIN, J.C., PERSON, A., IATZOURA, A., FERRĖ, B. & RENARD, M. (2000): Manganese in Pelagic carbonates: indication of major Tectonic events during the geodynamic evolution of a passive con- tinental margin (the Jurassic European Margin of the Tethys–Ligu- rian Sea).– Palaeogeogr., Palaeoclimat., Palaeoecol., 156, 123–138. doi:10.1016/S0031-0182(99)00135-2 CROATIAN GEOLOGICAL SURVEY (2009): Geološka karta Repub- like Hrvatske 1:300.000 [Geological Map of the Republic of Croatia 1:300 000 – in Croatian].– Zagreb. D’ARGENIO, B. & MINDSZENTY, A. (1995): Bauxites and related palaeokarst: tectonic and climatic event markers at regional uncon- formities.– Eclogae Geol. Helv., 88, 453–499. DAVIS, J.C. (1986): Statistics and data analysis in geology.– John Wiley & Sons, New York, 646 p. DE VOS, W., TARVAINEN, T. (Chief-editors), SALMINEN, R., REEDER, S., DE VIVO, B., DEMETRIADES, A., PIRC, S., BATISTA, M.J., MARSINA, K., OTTESEN, R.-T., O'CONNOR, P.J., BIDOVEC, M., LIMA, A., SIEWERS, U., SMITH, B., TAY- LOR, H., SHAW, R., SALPETEUR, I., GREGORAUSKIENE, V., HALAMIĆ, J., SLANINKA, I., LAX, K., GRAVESEN, P., BIRKE, M., BREWARD, N., ANDER, E.L., JORDAN, G., DURIS, M., KLEIN, P., LOCUTURA, J., BEL-LAN, A., PASIEC- ZNA, A., LIS, J., MAZREKU, A., GILUCIS, A., HEITZMANN, P., KLAVER, G. & PETERSELL, V. (2006): Geochemical Atlas of Europe. Part 2 – Interpretation of Geochemical Maps, Addi- tional Tables, Figures, Maps, and Related Publications, Geologi- cal Survey of Finland, 690 p. DILLON, W.R. & GOLDSTEIN, M. (1984): Multivariate analysis: methods and applications.– John Wiley & Sons, New York, 575 p. DOORNKAMP, J.C. & KING, C.A.M. (1971): Numerical analysis in geomorphology: an introduction.– Edward Arnold, London, 368 p. DRAGIČEVIĆ, I. & VELIĆ, I. (2002): The northeastern margin of the Adriatic Carbonate Platform.– Geol. Croat., 55/2, 185–232. ECONOMOU-ELIOPOULOS, M. (2003): Apatite and Mn, Zn, Co-en- riched chromite in Ni-laterites of northern Greece and their genetic signifi cance.– J. Geochem. Explor., 80, 41–54. doi:10.1016/S0375- 6742(03)00181-X FORCE, E.R. (1991): Geology of Titanium-Mineral Deposits.– GSA Spec. Pap., 259, 112 p. HALAMIĆ, J. & MIKO, S. (2009): Geochemical Atlas of the Republic of Croatia.– Croatian Geological Survey, Zagreb, 88 p. HOSE, H.R. (1986): Mediterranean karst bauxite genesis and plate tec- tonics during the Mesozoic.– In: 4th International Congress for the Study of Bauxite, Alumina and Aluminum (ICSOBA), Athens. Pro- ceedings, 333–341. HUGGET, R.J. (1998): Soil chronosequences, soil development and soil evolution: a critical review.– Catena, 32, 155–172. doi:10.1016/ S0341-8162(98)00053-8 HERRMANN, L., ANONGRAK, N., ZAREI, M., SCHULER, U. & SPOHRER, K. (2007): Factors and processes of gibbsite formation in Northern Thailand.– Catena, 71, 279–291. doi:10.1016/j.cate- na.2007.01.007 HIERONYMUS, B., KOTSCHOUBEY, B. & BOULÈGUE, J. (2001): Gallium behaviour in some contrasting lateritic profi les from Cam- eroon and Brasil.– J. Geochem. Explor., 72, 147–163. doi:10.1016/ S0375-6742(01)00160-1 HUERTA-DIAZ, M.A. & MORSE, J.W. (1992): Pyritization of trace metals in anoxic marine sediments.– Geochim. Cosmochim. Ac., 56, 2681–2702. doi:10.1016/0016-7037(92)90353-K KETZER, J.M., MORAD, S. & AMOROSI, A. (2003): Predictive dia- genetic clay-mineral distribution in siliciclastic rocks within a se- quence stratigraphic network.– Int. Assoc. Sedimentol. Assoc. Spec. Publ., 34, 43–51. KLEBER, M., SCHWENDENMANN, L., VELDKAMP, E., RÖSSNER, J. & JAHN, R. (2007): Halloysite versus gibbsite: silicon cycling as a pedogenetic process in two lowland neotropical rain forest soils of La Selva, Costa Rica.– Geoderma, 138, 1–11. doi:10.1016/j.ge- oderma.2006.10.004 KORBAR, T. (2009): Orogenic evolution of the External Dinarides in the NE Adriatic region: a model constrained by tectonostratigraphy of Upper Cretaceous to Paleogene carbonates.– Earth-Sci. Rev., 96, 296–312. doi:10.1016/j.earscirev.2009.07.004 Geologia Croatica 65 Kovačević Galović et al.: Geochemical discrimination of Early Palaeogene bauxites in Croatia KRUMBEIN, W.C. & GREYBILL, F.A. (1965): An introduction to sta- tistical models in geology.– McGraw-Hill, Toronto-London-Syd- ney, 475 p. MACLEAN, W.H. & BARRETT, T.J. (1993): Lithogeochemical techni- ques using immobile elements.– J. Geochem. Explor., 48, 109–133. doi:10.1016/0375-6742(93)90002-4 MATSCHULLAT, J., OTTENSTEIN, R. & REIMANN, C. (2000): Ge- ochemical background – can we calculate it?– Environ. Geol., 39/9, 990–1000. doi:10.1007/s002549900084 MATIČEC, D., VLAHOVIĆ, I., VELIĆ, I. & TIŠLJAR, J. (1996): Eocene limestone overlying Lower Cretaceous deposits of Western Istria (Croatia): did some parts of present Istria form land during the Cretaceous?– Geol. Croat., 49/1, 117–127. MERINO, E. & BANERJEE, A. (2008): Terra Rossa Genesis, Implica- tions for Karst, and Eolian Dust: A Geodynamic Thread.– J. Geol., 116, 62–75. doi:10.1086/524675 ÖZLÜ, N. (1983): Trace element contents of karst bauxites and their pa rent rocks in the Mediterranean belt.– Miner. Deposita, 18, 469–476. PALMER, M.R. (1985): Rare earth elements in foraminifera tests.– Earth Planet. Sc. Lett., 73, 285–298. doi:10.1016/0012-821X(85)90077-9 PAMIĆ, J., TOMLJENOVIC, B. & BALEN, D. (2002): Geodynamic and petrogenetic evolution of Alpine ophiolites from the central and NW Dinarides: an overview.– Lithos, 65, 113–142. doi:10.1016/ S0024-4937(02)00162-7 PEH, Z. & HALAMIĆ, J. (2010): Discriminant function model as a tool for classifi cation of stratigraphically undefi ned radiolarian cherts in ophiolite zones.– J. Geochem. Explor., 107, 30–38. doi:10.1016/j. gexplo.2010.06.003 PHILLIPS, J.D. (1999): Earth surface systems: complexity, order, and scale.– Blackwell, Malden, 180 p. REIMANN, C. & FILZMOSER, P. (2000): Normal and lognormal data distribution in geochemistry: death of a myth. Consequences for the statistical treatment of geochemical and environmental data.– Env. Geol., 39/9, 1001–1014. doi:10.1007/s002549900081 REIMANN, C., FILZMOSER, P. & GARRET, R.G. (2005): Back- ground and threshold: critical comparison of methods of determi- nation.– Sci. Total Environ., 346, 1–16. doi:10.1016/j.scitotenv. 2004.11.023 ROCK, N.M.S. (1988): Lecture Notes in Earth Sciences, 18: Numerical Geology.– Springer Verlag, Berlin, 427 p. SAKAČ, K., ŠINKOVEC, B. & GABRIĆ, A. (1978): Geologija i pa- leogenski boksiti Moseć planine (Dalmacija, južna Hrvatska) [Geological setting and bauxites of Mt. Moseć, Dalmatia (south Croatia) – in Croatian, with an English Abstract].– Geol. vjesnik, 30/1, 199–218. SAKAČ, K., ŠINKOVEC, B., JUNGWIRTH, E. & LUKŠIČ, B. (1984): Opća obilježja geološke građe i ležišta boksita područja Imotskog [General characteristics of geological framework and bauxite de- posits of Imotski area - in Croatian].– Geol. vjesnik, 37, 153–174. SAKAČ, K. & ŠINKOVEC, B. (1991): The bauxites of the Dinarides.– Travaux, 23, 1–12. SHELDON, N.D. & TABOR, N.J. (2009): Quantitative paleoenviron- mental and paleoclimatic reconstruction using paleosols.– Earth- Sci. Rev., 95, 1–52. doi:10.1016/j.earscirev.2009.03.004 StatSoft, Inc., 2006. STATISTICA (data analysis software system), ver- sion 7.1. www.statsoft.com ŠEBEČIĆ, B., PALINKAŠ, L., PAVIŠIĆ, D., ŠEBEČIĆ, B. & TRUTIN, M. (1985): Bauxite occurrences in the region of Zavojane and north- wardly of Imotski.– Geol. vjesnik, 38, 191–213. ŠINKOVEC, B. (1973): The origin of Early Palaeogene bauxites of Is- tria, Yugoslavia.– Travaux, 3, 151–164. ŠINKOVEC, B. & SAKAČ, K. (1981): Boksiti starijeg paleogene na otocima sjevernog Jadrana [The Early Paleogene Bauxites of North Adriatic Islands – in Croatian, with an English Abstract].– Geol. vjesnik, 33, 213–225. ŠINKOVEC, B. & SAKAČ, K. (1991): Bauxite deposits of Yugoslavia – the state of the art.– Acta Geologica Hungarica, 34/4, 307–315. ŠINKOVEC, B., SAKAČ, K. & DURN, G. (1994): Pyritized bauxites from Minjera, Istria, Croatia.– Nat. Croat., 3/1, 41–65. ŠUŠNJARA, A., SAKAČ, K., GABRIĆ, A. & ŠINKOVEC, B. (1990): Boksiti područja Sinja u Srednjoj Dalmaciji [Bauxites in the Sinj area in Middle Dalmatia - in Croatian, with an English Abstract].– Geol. vjesnik, 43, 169–179. TARDY, Y., TROLARD, F., EOQUIN, C. & NOVIKOFF, A. (1990): Distribution of hydrated and dehydrated minerals in lateritic profi - les and landscapes.– In: Geochemistry of the Earth’s surface and of mineral formation, 2nd International Symposium, July, 2–8, 1990, 133–136. TAYLOR, S.R. & MCLENNAN, S.M. (1985): The Continental Crust: its Composition and Evolution.– Blackwell Scientifi c Publications, 312 p. TIŠLJAR, J., VLAHOVIĆ, I., VELIĆ, I. & SOKAČ, B. (2002): Carbon- ate platform megafacies of the Jurassic and Cretaceous deposits of the Karst Dinarides.– Geol. Croat., 55/2, 139–170. VALETON, I., BIERMANN, M., RECHE, R. & ROSENBERG, F. (1987): Genesis of nickel laterites and bauxites in Greece during the Jurassic and Cretaceous, and their relation to ultrabasic parent rocks.– Ore Geol. Rev., 2, 359-404. doi:10.1016/0169-1368(87)90011-4 VLAHOVIĆ, I., TIŠLJAR, J., VELIĆ, I. & MATIČEC, D. (2002): The Karst Dinarides are composed of Relics of a single Mesozoic Plat- form: Facts and Consequences.– Geol. Croat., 55/2, 171–183. VLAHOVIĆ, I., TIŠLJAR, J., VELIĆ, I. & MATIČEC, D. (2005): Evo- lution of Adriatic Carbonate Platform: Palaeogeography, main events and depositional dynamics.– Palaeogeogr., Palaeoclimat., Palaeoecol., 220, 333–360. doi:10.1016/j.palaeo.2005.01.011 Manuscript received August 31, 2011 Revised manuscript accepted October 28, 2011 Available online February 25, 2012 Geologia Croatica 66 Geologia Croatica 65/1